What is the molar mass of a substance

Molar mass of a molecule is the sum of the atomic mass of the individual elements in the molecule.  

Atomic mass of Pb = 207  amu

Atomic mass of N = 14  amu

Atomic mass of O = 16  amu

Here amu stands for atomic mass unit

Molar mass of Pb(NO₃)₂ = 207 + [14 + (16 x 3)] x 2  

                                         = 207 + 28 + (48) x 2 = 331 g/mol  

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